C-scan testing

Possible nondestructive testing techniques for adhesively bonded structures and composite materials will be introduced along with a literature survey of successes and applications to date. Emphasis on ultrasonic inspection will also be highlighted, including such topics as ultrasonic wave generation, wave velocity, dispersion, reflection factor, wave refraction, attenuation, ultrasonic field analysis, resolution, thickness and defect location measurement, and C-scan testing. 

K. Subramanian and J. L. Rose, C-scan testing for complex parts. Conference of American Society of Metals, Orlando, Florida, October 4—9, 1986, Advanced Materials and Processes, Vol. 131, Issue 2 (February 1987). 

The benefit of such a model is that better understanding of the wave propagation process may be gained. Also, it is possible to make controlled parameter studies in order to understand the influence of e.g. defect orientation, probe angle and frequency on the test results. Results may be presented as A-, B- or C-scans. 

Depending on the requirements, C-scan or a cascading display are used. These types of display facilitate tests for internal damage below the surface with low-frequency eddy currents in addition to high-frequency tests for surface cracks. 

In addition to the distortions caused by the probes, there were also distortions caused by filtering the signals within the eddy-current test instruments. To achieve the highest possible dynamics with the test instruments, high-pass filters with a high rate of rise, but also a long reverberation time were used. Thus, the recorded C-scan pictures sometimes shows strong echo effects. 

Additional assistance is provided by secondary modification options that allow among others for a depiction of the original signal, the reconstruction of the depiction of the impedance plane of the eddy-current signals or for modifications of phase, amplification or zero point virtually in real time. That way, once C-scan images have been recorded, they can now be evaluated as needed without having to repeat the test. 

Mephisto is devoted to predict the ultrasonic scans (A,B or C-scans) for a priori knowledge of the piece and the defects within. In the present version Mephisto only deals with homogeneous isotropic materials. The piece under test can be planar, cylindrical or have a more complex geometry. The defects can be either planar (one or several facets), or volumetric (spherical voids, side drilled holes, flat or round bottom holes). 

Materials that in themselves are normally stable, even under fire conditions Materials that exhibit an exotherm at temperatures greater than 500°C when tested by differential scanning calorimetry (DSC) Materials that do not react with water heat of mixing less than 30 cal/g Less than 0.01 W/mL... 

Bonded structures that are ultrasonically tested by the immersion methods often use a C-scan recorder to record the test. This recorder is an electric device that accepts signals from the pulser-receiver and prints out a plan view of the part. The ultrasonic search unit is automatically scanned over the part. The ultrasonic signals for bond or unbond are detected from built-in reference standards. C-scan NDT techniques are used extensively by aircraft manufacturers to inspect bonded parts. 

Standard ASTM potentiodynamic anodic polarization plot for certification of potentiostat performance. Type 430 stainless steel in 1 N H2S04at 30 °C. Scan rate of 600 mV/h. Test curve is to lie within the shaded region. Redrawn from Ref 27... 

To quantify the results a combination of the signal amplitude of the interfacial echo (IE) in a C-scan, expressed through a colour code, and the adhesion strength obtained destructively by an ASTM C633-13 (2013) tensile test can be used. Echo-impulse techniques with an auxiliary reflector, for example by using water as an immersion medium allow measuring reliably the adhesion of very thin coatings... 

The resin content in both composites is about 37% by weight. The porosity of the composites was characterized by ultrasonic C-scans. The test specimens of no measurable porosity were used. The resin specimens and the composite laminates were cured in a hydraulic press at 250 F and 75 psl for one hour, and subsequently postcured at the same temperature in the absence of pressure for another two hours. Additional curing for up to 16 hours in the case of HX-205 and F-185 resins showed no measurable changes in dynamic mechanical properties. 

Mode I cyclic compression—compression tests on CFRP-impacted CFRP plates have been performed by Katerelos et al. [38]. The analysis relies on nondestructive testing (ultrasonic C-scan) and modelling for quantification of delamination resistance. In mode II tests, there is a choice between test parameters yielding no shear reversal or... 

The degradation of the composite laminates can be modelled as simple strength criteria for fibres or matrix, before delamination occurs. Eigure 9.19 shows the test force history for a 200 x 200 mm plate and the various numerical EE (77) predictions (Davies et al. [42]), The hnear elastic case does get the time of the event but underestimates the peak force by a factor of 3. The damaged EE prediction overestimates the force but does get the departure from the linear solution correctly. The fuUy degraded solution (with much fibre failure) does match the experimental history. Delamination was confined to one interface near the mid-plane as the C-scan image indicates. 

In a subsequent paper [67], subpenetration impact testing and ultrasonic C-scanning/optical reflection microscopy were used to characterize the damage in the three Epikote 828 resin-based laminates. At impact energies as low as 1.75 J mm , the damage zone was identified as the classic cone-of-fracture , that is more extensive delamination was sustained towards the unimpacted surface. 

The laminates of tiK carbon-fiber composite were first characterized by acoustic NDI (C-scan) and optical microscopy to evaluate their quality. Scanning electron microsctqiy (SEM) was used to evaluate laminate quality and nanoparticle distributimi using a Philips XL30 ESEM TMP scanning electron microscope. Mechanical tests fm tiie carbon-fiber composite were selected to measure resin-dominated properties. These tests were transverse four-point flexure with a qian-to-deptii ratio of 32 1 and longitudinal four-point flexure with a qi>an-to-depdi ratio of 16 1 designed to induce mic lane shear failure. Ten qiecimens were tested for each material type and condition. 

Images are typically displayed as either C-scans or B-scans. A C-scan is an overall X, Y view of the test specimen at a particular depth or interface. A color scale or black and white image displays signal amplitude. B-scans display an image of a cross-sectioned view at a chosen location with the scan indicating signal amplitude. Acoustic microscopes have the flexibility to adapt different transducers for different applications from low-frequency... 

Figure 17.94 Ultrasonic C-scan of cfrp laminate showing an area of impact induced delamination white indicates negligible damage and black bad damage. Source Reprinted from Cawley P, The sensitivity of the mechanical impedance method of nondestructive testing, NDT Int, 30(4), 209-215, Aug 1987.

C-scan C-scan is the back and forth scanning of a specimen with ultrasonics. It is a nondestructive testing technique for finding voids, delamination, defects in fiber distribution, etc. in laminates and other composite structures. 

---